1. Field of the Invention
The present invention relates to coated particles and to methods of making and using them. These coated particles have application in the release of one or more materials into selected environments, the absorption of one or more materials from selected environments and the adsorption of one or more materials from selected environments.
2. Related Art
Two particle technologiesxe2x80x94polymer-coated particles and liposomesxe2x80x94are of general interest.
Polymer-coated particles exhibit several limitations, as the flattened and diffuse response of their polymer coatings to chemical and physical triggers indicates. This is due to two factors. First, the high molecular weight of polymers reduces their diffusion coefficients and their kinetics of solubilization. Second, the neighboring group effect broadens the curves representing the chemical responses to triggers such as, inter alia, pH, salinity, oxidation and reduction, ionization, etc. (The neighboring group effect indicates that chemical changes in one monomeric unit of a polymer significantly alter the parameters governing chemical transitions in each of the neighboring monomeric units.) Further, most polymers are collections of chemical species of broadened molecular weight distribution. In addition, for a given application of the polymer-coated particle only a limited number of suitable polymers are frequently available. This is due to a number of factors: regulatory issues: the coating processes often entail harsh chemical and/or physical conditions, such as solvents, free radicals, elevated temperatures, dessication or drying, and/or macroscopic shearing forces needed to form the particles: the mechanical and thermal stabilities of the polymeric coatings in industrial applications are limited and further there is the adverse environmental impact of the large scale application of polymer-coated particles, such as in agricultural use.
Liposomes also exhibit a number of limitations. Among these are their physical and chemical instabilities. The release of a material disposed within the liposome is usually dependent on the destabilization of the structure of the liposome. In particular, the absence of porosity precludes the pore-controlled release of such materials. The dual requirements of 1) physical stability of the liposome until release is desired on the one hand and 2) release of materials by bilayer destabilization when release is desired on the other are problematic. (The term liposomes is frequently interchanged with the term vesicles and is usually reserved for vesicles of glycerophospholipids or other natural lipids. Vesicles are self-supported closed bilayer assemblies of several thousand lipid molecules (amphiphiles) that enclose an aqueous interior volume. The lipid bilayer is a two-dimensional fluid composed of lipids with their hydrophilic head groups exposed to the aqueous solution and their hydrophobic tails aggregated to exclude water. The bilayer structure is highly ordered yet dynamic because of the rapid lateral motion of the lipids within the plane of each half of the bilayer.) See O""Brien. D. F. and Ramaswami. V. (1989) in Mark-Bikales-Overberger-Menges Encyclopedia of Polymer Science and Engineering, Vol. 17, 2nd Ed., John Wiley and Somns. Inc., p. 108.
It is an object of the invention to provide coated particles that are suitable for solubilizing or containing a wide variety of materials, including materials sensitive to physical, chemical or biological deterioration.
It is an object of the invention to provide coated particles that release one or more materials disposed within a matrix in their internal cores without requiring the destabilization of that matrix.
It is an object of the invention to provide coated particles that sharply initiate the release or absorption of one or more materials to or from a selected environment in response to one or more physical or chemical triggers.
It is an object of the invention to provide coated particles that provide a wide variety of coated particle systems that can be tailored to the particular physical, chemical and biological requirements of their contemplated use, such as mechanical and thermal stability in industrial applications of the coated particles or freedom from adverse environmental impact in large scale application of the coated particles in agricultural use.
It is an object of the invention to provide coated particles that provide, if desired, a porous coating that permits pore-controlled release of materials disposed within them or pore-controlled absorption of materials disposed without them.
It is a still further object of the invention to provide coated particles that can be made by a simple process, including, preferably, without entailing harsh physical and/or chemical conditions.
The foregoing and other objects are provided by a coated particle that comprises an internal core comprising a matrix and an exterior coating. The matrix consists essentially of at least one nanostructured liquid phase, or at least one nanostructured liquid crystalline phase or a combination of the two and the exterior coating comprises a nonlamellar crystalline material.
In a preferred embodiment, the coated particle may be made by
1. providing a volume of the matrix that includes at least one chemical species having a moiety capable of forming a nonlamellar crystalline material upon reaction with a second moiety and
2. contacting the volume with a fluid containing at least one chemical species having the second moiety under nonlamellar crystalline material-forming conditions so as to react the first moiety with the second moiety and contemporaneously subdividing the volume into particles by the application of energy to the volume.
Alternatively, the coated particle can be made by
1. providing a volume of the matrix that includes a material in solution in it that is capable of forming a nonlamellar crystalline material that is insoluble in the matrix and
2. causing the aforesaid material to become insoluble in the matrix and contemporaneously subdividing the volume into particles by the application of energy to the volume.
Or, alternatively, a combination of these two methods can be applied.